What’s On the Bench Tonight (OBT)

[twocents]

Thanks X, that is very encouraging.

Do I perceive something – are you busy falling in love with tube gear and sound?

 

[xrk971]

Tubes are nice but mostly this is all specified by my customer’s requirements.

 

[puijkh]

Experimenter boards have arrived. JLC PCB is the fastest. They look nice too.

Now waiting for my M2x boards from the diyaudio shop (shipping takes weeks / months). Hope they arrive soon, so i can start experimenting

 

[xrk971]

Those look really nice and handy to have - great work!

 

[nigelwright7557]

I built up a new USB PC oscilloscope pcb.
When I tried to program the PIC it said cant read ID of device.
So re-soldered PIC and buzzed out basic connections for programming and it was fine.
I removed anything that was connected to PIC in case they were interfering but no joy.
So I swapped out PIC and still no joy.
So gave up on it and scrapped pcb, hot air removed anything of value.
Built up new pcb with old components and it worked first time !
Sods law I guess.

 

[xrk971]

Don’t you hate it when that happens!? I have wasted days on a board, just to a abandon and start anew. It generally works first time on the second board.

How does the scope work out for you?

 

[xrk971]

LuFo is on Vunce’s bench I know. From what I hear, it seems first power up was uneventful. Always a good thing!

 

[peppennino]

Great!

 

[xrk971]

I just got back from vacation and these fine looking OPA454 and +/-35v DCDC booster power supply boards were waiting for me. I may have to do some SMT soldering tonight!

 

[xrk971]

WOBT June 23, 2021: SMT assembly of the +/-35v DC/DC converter board for the LuFo OPA454 front end (FE) board. This is using an LT8364 SEPIC topology which is nice in that the output is galvanically isolated from the input.

 

[xrk971]

Experimenter boards have arrived. JLC PCB is the fastest. They look nice too.

Now waiting for my M2x boards from the diyaudio shop (shipping takes weeks / months). Hope they arrive soon, so i can start experimenting

Hi Puijkh,

Thanks so much for sending me some boards and even a set of purple boards with ENIG from OSH. They are super premium looking!

These will be very handy to have around to try new designs.

 

[xrk971]

WOBT June 25, 2021: Assembled the OPA454 Front End board for the LuFo amp. It fits on top of the PSU board nicely.

 

[xrk971]

The OPA454 works! It’s singing away and sounds great. Very quiet too. Cannot tell it is turned on.

 

[xrk971]

On the bench tonight is a simple dynamic microphone preamp. I got the circuit from Elliot Sound Products (ESP) website. I happened to pick one (project 113 figure 3) that was not verified but Rod Elliot said:

This version has not actually been built and used in earnest, but has been simulated and is a viable proposition - it can be expected to work as described without problems.

Famous last words…

Well it is missing a bypass cap across the power rail pins, needs a 220pF compensation cap across the 50k feedback resistor, and needs a 47k load on the output. It’s amplifying sound and works now but I could not get it to work with a TL071CP. I finally switched to NJM5534D and at least it doesn’t swing wildly rail to rail and makes sound.

This is a project that I am helping my neighbor build for his home recording studio setup. Simple projects like this never are simple.

Schematic as given:

 

[puijkh]

Hi Puijkh,

Thanks so much for sending me some boards and even a set of purple boards with ENIG from OSH. They are super premium looking!

These will be very handy to have around to try new designs.

The after dark from Osh park look really good.
I also recieved the enig ones from Aisler (about 2 weeks production time).
I am compairing different pcb vendors. The Seeed pcb's are still in transit.

 

[twocents]

This is a project that I am helping my neighbor build for his home recording studio setup. Simple projects like this never are simple.

So true! I have been caught many times, trying to help friends or family. On my bench for the last few months now – a simple arduino based diy RC Transmitter and Receiver, for a friend's teenage boy. A nice project, but it’s not working. How to figure out where the problem lies – the transmitter, the receiver, or the code? Only way to find out - to build more and test more. But it robs precious diy audio time!

 

[xrk971]

The secret with Arduino projects is to find a YouTube video where someone has done almost exactly what you are trying to do. That always works for me. Sometimes there are pretty good howto websites by someone who has done it. I’m pretty sure the Arduino RF Tx/Rx is well-trodden.

I finally got the mic preamp to work. There’s no way this could have been done without an O-scope (a critical tool for any bench). I found oscillation at 13MHz and another at 2MHz. There was a massive rail to rail oscillation with TL071CP which went away when I used NJM5534D. I am using two 9v batteries for 18v rail and it works fine like that. Super quiet when powered with batteries too. It required two 220pF film compensation caps, a series resistor at the output of the opamp buffer, and changing to a BJT input opamp before it worked. But now that it works, it sounds beautiful. Super quiet , nice variable gain up to 32dB and now I know how to make a nice mic preamp. But yes, there went 4 hours of DIY audio projects time for my own stuff. But hey, I learned something, and I appreciate Rod Elliot for putting so much content out there for all of us to use for free. I go his site all the time to see how to do stuff like this.

Here is the circuit as built that now works great.

 

[xrk971]

And I thought I was the only one crazy enough to literally "cook up" some SMD boards in a frying pan. I used a similar pan on a $15 "Aroma" brand hot plate that I got from Amazon.

I was advised that the fumes coming from overheated Teflon are quite toxic, so I switched to a piece of 0.100 inch thick aluminum held in a pair of Vise Grips. I think it works better since it is flatter. As soon as the solder reflows I move the aluminum from the hot plate to a large heat sink for cooling. I will be cooking up some SMD modules for my Eurorack synthesizer in the near future.

For now, a new UNSET SE tube amp board is on the test bench, and a few more are on the build bench. These use all through hole parts.

The UNSET is a new SE tube amp design, and this one is making 30 watts at 2.5% THD, and 60 very distorted watts when driven about 10 dB harder.

UNSET is coming?

Hi Tubelab,
How is your UNSET testing coming along? Looks like a really cool amp - looking forward to seeing it fully working.

I have a question for you, is there a good source of a lot of 7370 tubes somewhere?

Thanks,
X

 

[xrk971]

WOBT June 30, 2021: assembling the chassis for the LuFo amp. This is the first channel. It all fits perfectly. This thing is built like a German tank. Very nicely done.

Nearly 23lbs each:

 

[xrk971]

On the bench tonight - 4th of July, 2021: testing a new phono preamp design by Jhofland and layout by JPS64 on an LSA T2 TT with a Sumiko Blackbird MC cartridge. Using the LSA HyperSET hybrid tube preamp to drive DIYA VFET amp and 10F/RS225 TL speakers. Pink Floyd sounds amazing. This record gives me chills/goosebumps-good kind of a music experience.